The European Union (Notification of Withdrawal) Bill is set to be debated by MPs on Monday, when they will decide whether to accept two amendments added by the House of Lords.
On Tuesday, the Prime Minister will brief MPs in the Commons about this week’s EU summit, and it is understood she may use the occasion to formally trigger the leaving process.
One of the amendments voted through by the House of Lords would force the Government to give MPs a “meaningful vote” on the final Brexit deal before the country withdrew from the bloc.
The other change asks the Government to guarantee the rights of EU citizens when it leaves.
Ms May has committed the Government to triggering Article 50 by the end of March, which leaves less than three weeks in which to pull the trigger.
But unnamed Westminster sources have reportedly said that the action could come as soon as Tuesday or Wednesday next week.
If the Brexit bill does not pass smoothly through the Commons, upcoming elections in the Netherlands may force the Prime Minister to delay until the end of the month.
Meanwhile, Labour has made a “direct appeal” for Ms May to allow the bill’s two changes to pass.
In a letter, the party called on the Prime Minister to give in to demands for a “meaningful” parliamentary vote on the final exit package and guarantee protections for EU nationals living in Britain.
Peers defeated the Government on both issues but MPs are expected to overturn the changes when the Brexit bill returns to the House of Commons next week.
The letter, sent by shadow Brexit Secretary Sir Keir Starmer and Baroness Smith, shadow leader of the Lords, said the changes would not damage the PM’s plans to trigger Article 50 by the end of the month.
It said: “Labour supported both these amendments in the House of Commons. Labour peers both led and helped pass them in the House of Lords, and Labour will continue to fully support these amendments on Monday.
“You will understand, however, our concerns that government ministers (including David Davis in the House of Commons yesterday during the Exiting the EU oral questions) have indicated they will simply ignore these amendments and seek to delete them from the bill, before any debate or consideration in the House of Commons on the substantive issues raised in the Lords debates.
“Surely the issues raised in the Lords and such large majorities from across the House are worthy of greater consideration?
“We are making this direct appeal to you and hope that you will give it your urgent personal attention.”
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